The present invention relates to an engine system and more particularly to an engine system having an internal combustion engine and an exhaust gas treatment system.
An engine system is known which comprises a three-way catalytic converter in which engine exhaust gases flowing therethrough are exposed to a catalytic substance which, given the proper air-fuel ratio in the exhaust gases, will promote simultaneous oxidation of CO and HC and reduction of NOx. In such an engine system, because an air fuel mixture supplier is so controlled as to effect combustion at stoichiometry, fuel economy is poorer than an engine system in which lean combustion takes place. Moreover, the known engine system can not yield power output high enough to meet demand when high power output is required.
Another known engine system comprises an oxidation catalytic converter which has a catalytic substance which will promote oxidation of CO and HC. In such an engine system, because an air fuel mixture supplier is so controlled as to effect lean combustion, fuel consumption increases and power output decreases when the engine operates under light load conditions. These results are attributable to the fact that the ratio of residual gas to fresh air fuel mixture in a charge in a combustion chamber increases abruptly under these conditions bringing about rough combustion leading to rough engine operation.